Powders are commonly used in cosmetic formulations to provide specific textures and sensory feel, especially for cosmetics and skin care applications. The powders used may be inorganic minerals (such as mica, talc, kaolin, silica, etc.), may be organic-based materials (such as starch, cellulose, jojoba, etc.), or may be synthetic polymer powders (such as polyamides, polyurethanes, acrylics, polymeric silicones, polyolefins, etc.). Polyurethane and silicone powders are often present in high end cosmetics, due to their elastomeric and rubbery properties. The powders may be surface treated to enhance their physical properties, improve dispersion, increase/decrease hydrophobicity, and improve dispersion.
Due to bulk microporosity found in some of these powders (such as found in Orgasol® powders from Arkema Inc.), they can also be used as carriers of active ingredients, including but not limited to hyaluronic acid, lactic acid, ceramide, glycerin, etc. Arkema's ORGASOL® ultra-fine polyamide powders are microporous, and have open cells due to their manufacturing process. These powders have a very narrow particle size range that can be between 5 and 60 microns, depending on the grade.
Expanded polymers, also known as polymer foams, provide lighter, softer and more flexible structures, with increased surface area, and lower density. Polymer foams are used to provide thermal and acoustical insulation, as well as strong, lighter, lower density structures. Polymeric foams are generally formed, as described in U.S. Pat. No. 8,277,913, by melting the polymer, adding a chemical or physical blowing agent (directly or in a master batch), the blowing agent expands the volume of the melted polymer forming small voids, and when cooled, the gas bubbles are either trapped (in a closed cell foam), or dissipate to create inter-connected voids (in an open cell foam). Polyamide foams are described, for example in U.S. Pat. Nos. 4,464,491, 4,028,287, 4,022,719 and 6,039,085
Unfortunately, the foams formed from a melt cannot be shredded, cut or ground in a manner to produce consistent foam particles in the 5 to 100 micron region. Even cryogenic grinding of foams does not result in small individual foam particles of the 5 to 100 micron range.
Polymer foams have been formed by methods other than from the melt. In U.S. Pat. No. 7,081,216, an open cell polymer foam was formed from a polymer latex or polymer aqueous suspension by first freezing the aqueous polymer dispersion or suspension, followed by thawing. This freeze-thaw polymer foam resulted in a large foam molded object, and not in individual, small polymer foam particles. US 2009/0048356 describes a process for introducing a gas into a polymer, in which polymer granules are exposed to an inert gas, under pressure and at a temperature between the glass transition (Tg) point and the melting point for a semi-crystalline or crystalline polymer, or a temperature below the Tg for an amorphous polymer. The gas impregnated polymer is then melt-processed, where the impregnated gas expands into a foamed, shaped article. A similar process is described in U.S. Pat. No. 7,994,231, in which a polyamide resin is subjected to high pressure under an inert gas, the temperature is raised to soften the polymer, the pressure is then lowered and temperature is lowered below the softening point, The partially expanded polyamide resin is again heated above its softening point under pressure, then the pressure reduced while the polymer remains above the softening point. This results in a closed cell polyamide film. The Examples are all done on polymer slabs.
It has now been found that polymeric powders can be expanded without undergoing a melt process, to produce very small, individual expanded powder particles in the 5 to 100 micron range. These expanded powders are lighter, softer and have more surface area (are more absorbent) than the solid polymer particles. The expanded polymer powders also exhibit elastomeric properties with improved compaction and cushioning, higher oil absorption, and higher active ingredient loading.